Impedance Balancing Noise Filtering Circuit for EMI Reduction

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Solution Overview

Problem

Electric drive systems generate high-frequency noise and harmonics leading to common mode electromagnetic interference (EMI) that negatively impacts both the load and power source, making it difficult to filter effectively.

Innovation Solution

An impedance balancing noise filtering circuit is introduced, featuring an impedance bridge and passive components on both the DC-side and AC-side of the inverter, which creates an impedance match to cancel common mode currents, reducing EMI emissions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional EMI filtering methods are used, then EMI noise is reduced, but device complexity and power loss increase

Engineering Contradiction:

ImproveEMI noiseVSAvoidfiltering circuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent changes the impedance parameters of the filtering circuit by using adjustable impedance elements that can be tuned to match the characteristic impedance of the transmission line. This impedance matching minimizes reflections and maximizes noise cancellation effectiveness, thereby reducing EMI noise while maintaining circuit simplicity

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces an intermediary impedance balancing circuit that acts as a mediator between the power converter and the transmission line. This intermediary circuit absorbs and dissipates common-mode noise currents through controlled impedance paths, preventing them from propagating and reducing EMI without requiring complex filtering components

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If conventional EMI filtering methods are used, then EMI noise is reduced, but power loss increases

Engineering Contradiction:

ImproveEMI noiseVSAvoidpower loss

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The patent optimizes the impedance parameters of the filtering circuit to minimize power loss. By adjusting the impedance values to match the transmission line characteristic impedance, the circuit achieves maximum power transfer and minimum reflections, thereby reducing EMI noise while minimizing resistive power losses in the filtering components

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful common-mode noise currents into useful information by measuring them through the impedance balancing circuit. The measured noise currents are then used to generate compensating signals that cancel the original noise, thereby eliminating EMI without dissipating power through traditional resistive filtering methods

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Object-generated harmful factors

If impedance balancing is implemented, then EMI emission is reduced, but device complexity increases

Engineering Contradiction:

ImproveEMI emissionVSAvoidcircuit configuration

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The patent segments the EMI filtering function into separate modular components: an impedance balancing network, a noise detection circuit, and a compensation circuit. Each module performs a specific function and can be independently optimized and adjusted, simplifying the overall design and implementation while achieving effective EMI reduction

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent designs the impedance balancing circuit to serve multiple functions simultaneously: it provides impedance matching for maximum power transfer, balances common-mode currents for noise cancellation, and provides a measurement path for noise detection. This multi-functionality reduces the need for separate dedicated components, thereby reducing overall device complexity while achieving EMI emission reduction

Inventive Principle:

Principle #6Universality (Multi-functionality)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution significantly reduces weight, volume, and power loss in electric drive systems, enhancing performance by providing filtered AC power with minimized EMI noise, thus improving specific power and efficiency.

Implementation Method 1

These sets of passive components are configured to facilitate impedance balancing that reduce common-mode (CM) electromagnetic interference (EMI) emission at the output port of the DC power source

Methodology Applied

Scientific EffectImpedance matching: Electrical Impedance Tomography

Data Source

PatentUS11608186B2Impedance balancing for noise filtering in electric drive systems

Publication Date: 2023.03.21 THE BOEING CO

AI summary

An electric drive system including an impedance balancing noise filtering circuit is disclosed. The electric drive system includes a direct current (DC) power source configured to output DC power to an output port and an inverter configured to convert the DC power output by the DC power source into alternating current (AC) power that is provided to an input port of an AC load. The impedance balancing noise filtering circuit includes an impedance bridge electrically intermediate the output port of the DC power source and the input port of the AC load. The impedance balancing noise filtering circuit includes different sets of passive components that are positioned on both the DC-side and the AC-side of the inverter. These sets of passive components are configured to facilitate impedance balancing that reduces common-mode (CM) electromagnetic interference (EMI) emission at the output port of the DC power source.